An existing arrangement for producing synthetic rock precursor incorporating high level radioactive waste involves the production of synthetic rock precursor using tetraisopropyltitanate and tetrabutylzirconate as ultimate sources of titanium oxide TiO.sub.2 and ZrO.sub.2. The components are mixed with nitrate solutions of other components, coprecipitated by addition of sodium hydroxide and then washed. The precursor thus produced is mixed in a hot cell with high level nuclear waste in the form of a nitrate solution to form a thick homogenous slurry. The slurry is then fed to a rotary kiln in which the slurry is heated, devolatilized and calcined to produce a powder which is then mixed with metallic titanium powder and poured into containers for hot pressing.
The containers which are used for this purpose have a generally cylindrical wall of bellows-like formation. Heat and pressure is applied to each container and its contents, and a synthetic rock product is formed within the container with the high level radioactive waste suitably immobilised therein.
A system for producing synthetic rock as described above has a number of deficiencies which will now be outlined.
The apparatus required to produce the synthetic rock requires that a slurry incorporating high level radioactive waste be fed into a calciner. The calciner must be free of oxygen by the use of a reducing gas and at the same time the slurry must be heated and dried.
A calciner which meets all these objectives is a large and cumbersome apparatus with numerous working parts on which it is difficult to perform maintenance on. Typically, a rabble bar is required within the calciner to prevent caking of the slurry and a filtration system is required to prevent escape of radioactive dust.
The present invention provides an alternative method for use in forming a substance incorporating immobilised radioactive waste.